Mike has taken apart a GFI Circuit Breaker and tested it to destruction. These devices are great to make electricity safer when used in dangerous environments such as beside water sources. They measure leakage current and trip when there is too much running from your hair dryer that accidentally fell into your tub full of water.
“A GFCI works by measuring the current leaving one side of a power source (the so-called “live” or “hot wire”), and comparing it to current returning on the other (the “neutral” side). If they are not equal, then some of the current must be leaking in an unwanted way, and the GFCI shuts the power off. After the problem is fixed, the device must be reset manually by pushing the reset button (the red button in the image shown at right). If the problem is not fixed, the GFCI will keep shutting off.”